Slider. Перелистывание изображенийй

var slideIndex = 1;
showSlides(slideIndex);
 
function plusSlide() {
    showSlides(slideIndex += 1);
}
 
function minusSlide() {
    showSlides(slideIndex -= 1);  
}
 
function currentSlide(n) {
    showSlides(slideIndex = n);
}
 
function showSlides(n) {
    let i;
    let slides = document.getElementsByClassName("item");
    let dots = document.getElementsByClassName("slider-dots_item");
    if (n > slides.length) {
      slideIndex = 1
    }
    if (n < 1) {
        slideIndex = slides.length
    }
    for (i = 0; i < slides.length; i++) {
        slides[i].style.display = "none";
    }
    for (i = 0; i < dots.length; i++) {
        dots[i].className = dots[i].className.replace(" active", "");
    }
    slides[slideIndex - 1].style.display = "block";
    dots[slideIndex - 1].className += " active";
}

let opSLider = {
  instances: Array.from(document.getElementsByClassName(`module-slider-auto`)),
  timer: null,
  events: {
    click: e => e.target.classList.contains(`left`) ?
    e.target.parentElement.insertBefore(e.target.nextElementSibling, e.target.parentElement.lastElementChild) :
    e.target.classList.contains(`right`) ?
    e.target.parentElement.insertBefore(e.target.previousElementSibling, e.target.parentElement.children[1]) : false,
    load: function t() {
      opSLider.tSlideDirection(`left`);
      opSLider.timer = setTimeout(t, 10000);
    }
  },
  tSlideDirection: direction => {
    opSLider.instances.forEach(e => direction === `left` ?
                               e.insertBefore(e.children[1], e.children[e.children.length - 2]) :
                               direction === `right` ?
                               e.insertBefore(e.children[e.children.length - 2], e.children[1]) : false);
  }
}
 
opSLider.instances.forEach(e => e.addEventListener(`click`, opSLider.events.click));
window.addEventListener(`load`,  opSLider.events.load);
window.addEventListener(`beforeunload`, () => {
  clearTimeout(opSLider.timer);
  window.removeEventListener(`load`,  opSLider.events.load);
  opSLider.instances.forEach(e => e.removeEventListener(`click`, opSLider.events.click));
  opSLider = undefined;
});